1. Field of the Invention
The present invention relates to a method of decomposing cleaning gas used for cleaning a film deposition chamber, in which a film for forming an electronic circuit device is deposited on a wafer. More particularly, the present invention relates to a method of decomposing cleaning gas used in a thin film deposition process for forming a functional component typified by a semiconductor device or a liquid crystal display device.
2. Background Art
A process for fabricating an electronic device, such as a semiconductor device or a liquid crystal element, has inevitably includes a process of depositing a thin film within a thin film deposition chamber. Such film may be a silicon oxide (SiO) film, a silicon nitride (SiN) film, a silicon (Si) film, a tungsten (W) film, or a tungsten silicide (WSi) film.
In the thin film deposition chamber, when a thin film is deposited on an element which is under manufacture, same film is gradually accumulated and stored within the thin film deposition chamber. Such accumulated film may be exfoliated from the chamber and become the source of dust, thereby involving a risk of increasing the amount of defects in the film used for forming an element. In order to prevent generation of the dust, the interior of the thin film deposition chamber must be periodically cleaned.
The cleaning gas is eventually emitted to the atmosphere. For example, in the case of nitrogen trifluoride (NF3), in a final emission phase the concentration of NF3 must be controlled to an allowable level of the order of ppm.
FIG. 8 is a descriptive view for describing the concept of conventional plant-wide gas exhaust facilities.
In FIG. 8, reference numeral 10 designates a thermal CVD system for depositing a tungsten film; 21 designates a pump; 22 designates an NF3 gas decomposer; 23 designates a plant-wide decomposer; and 24 and 25 designate other thin film deposition apparatus.
As shown in FIG. 8, an actual plant is equipped with a number of thin film deposition systems 10, 24, and 25, and the respective thin film deposition systems 10, 24, and 25 emit gases. The thus-emitted gases are collected in the plant-wide decomposer 23 connected to the thin film deposition systems 10, 24, and 25, where the gases are subjected to decomposing until they are brought to a safe exhaust level and are discharged to the atmosphere.
In this case, for example, the gas emitted from the CVD system 10 is decomposed by means of the stand-alone NF3 gas decomposer 22 which is specifically designed for removing NF3 and is disposed between the CVD system 10 and the plant-wide decomposer 23. After having been decomposed to a safe exhaust level at which it can be mixed with other gases, the gas is emitted to the plant-wide decomposer 23.
If no plasma is developed in the CVD system 10, the film deposition room cleaning gas is not decomposed, and the NF3 gas decomposer 22 is required to decompose the cleaning gas.
For example, in the case of a thin film deposition apparatus, such as the CVD system 10, at the time of purchase of the thin film deposition apparatus, the user must purchase a standalone gas decomposer specifically designated for use with the thin film deposition apparatus. Further, the user must bear costs for operating the gas decomposer.
The present invention has been conceived to solve these problems, and the object of the present invention is to provide a processing method which prevents emission of gas to be filtered at the time of cleaning of a processing system, reduces the toxicity of exhaust gas from a plant, and diminishes the necessity for an apparatus designated for filtering purpose.
According to one aspect of the present invention, in a method of decomposing a cleaning gas introduced into a film deposition chamber, a predetermined gas is introduced into the film deposition chamber and a plasma is developed before introduction of a cleaning gas in a preliminary process. The predetermined gas is different from the cleaning gas and is not required to be decomposed for evacuation. In a main process subsequent to the preliminary process, the cleaning gas is introduced into the the film deposition chamber, and plasma is developed to decompose the cleaning gas for cleaning a deposited film in the film deposition chamber, whereby the cleaning gas is evacuated while being substantially totally decomposed.
According to another aspect of the present invention, in a method of decomposing a cleaning gas introduced into a film deposition chamber, the cleaning gas is introduced into the the film deposition chamber, and plasma is developed to decompose the cleaning gas for cleaning a deposited film in the film deposition chamber in a main process. In a subsequent process, a predetermined gas is introduced into the film deposition chamber and development of plasma is continued subsequent to the main process. The predetermined gas is different from the cleaning gas and is not required to be decomposed for evacuation, whereby the cleaning gas is evacuated while being substantially totally decomposed.
In another aspect, the preliminary process, the main process and the subsequent process as described above may be combined in series.
Other and further objects, features and advantages of the invention will appear more fully from the following description.